What Is a Graphite Sheet Gasket?
A graphite sheet gasket is a soft (non-metallic) gasket made from expanded flexible graphite sheet material, cut to match the flange dimensions. Flexible graphite is produced by chemically treating natural graphite flakes (intercalation), then expanding them at high temperature to form worm-like particles that are compressed into sheets without binders or fillers. The result is a pure carbon sealing material with exceptional temperature resistance, chemical inertness, and conformability.
| Property | Value |
|---|---|
| Material | Expanded flexible graphite (>95% carbon) |
| Density | 1.0-1.8 g/cm3 (varies by grade) |
| Max temperature (oxidizing) | 450 degC (842 degF) in air |
| Max temperature (non-oxidizing) | 550 degC (1,022 degF) in steam/inert atmosphere |
| Min temperature | -200 degC (-328 degF); cryogenic capable |
| Standard | ASME B16.21 (non-metallic gaskets) |
| Compressibility | 40-50% (per ASTM F36) |
| Recovery | 10-15% |
Graphite Sheet Forms
Flexible graphite gaskets are available in three forms:
| Form | Construction | Typical Use |
|---|---|---|
| Homogeneous sheet | Pure graphite, no reinforcement | Low-pressure, moderate temperature |
| Metal-inserted sheet | Graphite bonded to SS 316 or SS 304 tanged metal core (0.05-0.1 mm) | Higher pressure, better blowout resistance, standard industrial use |
| Adhesive-backed sheet | Graphite with adhesive on one side | Easy installation on vertical flanges |
Metal-inserted (tanged) graphite is the most widely used form for industrial gaskets. The perforated metal insert prevents creep-related blowout and allows the gasket to maintain integrity during handling and installation.
Temperature and Pressure Ratings
| Graphite Grade | Metal Insert | Max Temp | Max Pressure | Application |
|---|---|---|---|---|
| Standard (1.0 g/cm3) | None | 450 degC (842 degF) | 20 bar (290 psi) | Low-pressure steam, utilities |
| Standard (1.0 g/cm3) | SS 316 tang | 450 degC (842 degF) | 80 bar (1,160 psi) | Process piping, heat exchangers |
| High-density (1.6 g/cm3) | SS 316 tang | 550 degC (1,022 degF) | 100 bar (1,450 psi) | High-temp steam, hydrocarbon |
| Nuclear grade (>99.5% C) | SS 316L tang | 550 degC (1,022 degF) | 100 bar (1,450 psi) | Nuclear, critical service |
In oxidizing atmospheres (air, oxygen), graphite begins to oxidize above 450 degC. In steam, inert gas (nitrogen, argon), or hydrocarbon atmospheres, it remains stable to 550 degC or higher. For oxidizing service above 450 degC, use mica-based gaskets instead.
Chemical Compatibility
Flexible graphite resists virtually all chemicals except strong oxidizing acids (concentrated HNO3, chromic acid, aqua regia) and molten alkali metals. It is compatible with:
- Hydrocarbons (crude oil, refined products, natural gas)
- Steam (saturated and superheated)
- Caustic solutions (NaOH, KOH)
- Dilute acids (HCl, H2SO4 at moderate concentrations)
- Hydrogen, ammonia, and most gases
For strong oxidizers, specify PTFE-based gaskets or PTFE filler in spiral wound gaskets.
Graphite vs PTFE Sheet Gaskets
| Property | Graphite Sheet | PTFE Sheet |
|---|---|---|
| Max temperature | 550 degC | 260 degC |
| Creep resistance | Good (with metal insert) | Poor |
| Chemical resistance | Good (except strong oxidizers) | Excellent (universal) |
| Sealability | Excellent (conforms to surface) | Good |
| Reusability | No | No |
| Cost | Moderate | Low |
Install graphite sheet gaskets with stud bolts torqued per ASME PCC-1 using the multi-pass star pattern described in the bolt torque guide.
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